[Bug python/11777] New: Strange behaviour of gdb.Type.fields

[Bug python/11777] New: Strange behaviour of gdb.Type.fields

[andre dot poenitz at nokia dot com]

I sometimes cannot get a proper list of members from structures that do have
members:


This accesses a "real" QRegionPrivate object in a 'QRegion region;':

  python print
gdb.parse_and_eval(\"region\")[\"d\"].dereference()[\"qt_rgn\"].dereference().type

  -> struct myns::QRegionPrivate
 
  python print
gdb.parse_and_eval(\"region\")[\"d\"].dereference()[\"qt_rgn\"].dereference().type.fields()

-> []


If I "create" the type manually I get:
 
  python print gdb.parse_and_eval(\"('myns::QRegionPrivate'*)0\").dereference().type
    -> myns::QRegionPrivate

  python print gdb.parse_and_eval(\"('myns::QRegionPrivate'*)0
\").dereference().type.fields()

    -> [<gdb.Field object at 0xb7764ac0>, <gdb.Field object at 0xb7764af0>,
<gdb.Field object at 0xb7764b20>, <gdb.Field object at 0xb7764b50>, <gdb.Field
object at 0xb7764b80>]

 
Note the extra "struct " in the 'type' output in the first case.

The problem also disappears when I use  type = gdb.lookup_type(str(type)) 
before accessing fields().

-- 
           Summary: Strange behaviour of gdb.Type.fields
           Product: gdb
           Version: 7.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: python
        AssignedTo: unassigned at sourceware dot org
        ReportedBy: andre dot poenitz at nokia dot com
                CC: gdb-prs at sourceware dot org
 GCC build triplet: i486-linux-gnu
  GCC host triplet: i486-linux-gnu
GCC target triplet: i486-linux-gnu


http://sourceware.org/bugzilla/show_bug.cgi?id=11777

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[Bug python/11777] Strange behaviour of gdb.Type.fields

[andre dot poenitz at nokia dot com]

------- Additional Comments From andre dot poenitz at nokia dot com  2010-07-01 07:35 -------
To reproduce:

mkdir x && cd x
echo -e "#include <QRegion>\nint main() { QRegion r; }" > 1.cpp
qmake -project && qmake && make
gdb -ex "b main" -ex "run" -ex "python import gdb" -ex 'python print
gdb.parse_and_eval("r")["d"].dereference()["qt_rgn"].dereference().type.fields()' -ex
'python print
gdb.lookup_type(str(gdb.parse_and_eval("r")["d"].dereference()["qt_rgn"].dereference().type)).fields()'
./x

-- 


http://sourceware.org/bugzilla/show_bug.cgi?id=11777

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[Bug python/11777] Strange behaviour of gdb.Type.fields

[andre dot poenitz at nokia dot com]

------- Additional Comments From andre dot poenitz at nokia dot com  2010-07-01 09:13 -------

To reproduce without Qt:


------------------------- snip ------------------------
mkdir x && cd x


echo -e "struct P { P(); int a, b, c, d; }; " > p.h
echo -e "#include \"p.h\"\n P::P() {} " > p.cpp
echo -e "class P; struct X { X(); P *p; };" > x.h
echo -e " #include \"x.h\"\n X::X() {} " > x.cpp
echo -e "#include \"x.h\"\n int main() { X x; }" > main.cpp

g++ -g -shared -o libxp.so x.cpp p.cpp
g++ -g -o x -L. -lxp main.cpp -Wl,-rpath,`pwd`

gdb -ex "b main" -ex "run" -ex "python import gdb" \
    -ex 'set confirm off' \
    -ex 'python print gdb.parse_and_eval("x")["p"].dereference().type.fields()' \
    -ex 'python print
gdb.lookup_type(str(gdb.parse_and_eval("x")["p"].dereference().type)).fields()' \
    -ex q \
    ./x
------------------------- snip ------------------------


-- 


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[Bug python/11777] Strange behaviour of gdb.Type.fields

[tromey at redhat dot com]

------- Additional Comments From tromey at redhat dot com  2010-07-06 19:52 -------
(In reply to comment #2)

>     -ex 'python print gdb.parse_and_eval("x")["p"].dereference().type.fields()' \

I can make this work by adding a call to strip_typedefs:



(gdb) python print gdb.parse_and_eval ('x')['p'].dereference().type.fields()
[]
(gdb) python print gdb.parse_and_eval
('x')['p'].dereference().type.strip_typedefs().fields()
[<gdb.Field object at 0xb7dbc220>, <gdb.Field object at 0xb7dbc250>, <gdb.Field
object at 0xb7dbc280>, <gdb.Field object at 0xb7dbc2b0>]


Arguably the Python API should be doing this for you.
It seems useless to get the fields of a stub type.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |tromey at redhat dot com


http://sourceware.org/bugzilla/show_bug.cgi?id=11777

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[Bug python/11777] Strange behaviour of gdb.Type.fields

[tromey at redhat dot com]

------- Additional Comments From tromey at redhat dot com  2010-08-20 18:27 -------


*** This bug has been marked as a duplicate of 10953 ***

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |DUPLICATE


http://sourceware.org/bugzilla/show_bug.cgi?id=11777

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